Pulmonary arterial hypertension (PAH) is a devastating disease with an estimated median survival of less than 3 years when left untreated. The recent development of effective medical therapy has begun to transform this once rapidly lethal disease into a condition characterized by chronic, progressive respiratory impairment. As with other chronic respiratory conditions, the goals of therapy have broadened to include patient-oriented outcomes, specifically health-related quality-of-life. Unfortunately, very limited information exists on the utility of quality-of-life measures in PAH and how they relate to other more established clinical outcomes. Furthermore, little is known about how psychosocial factors may also mediate the effect of treatment on quality-of-life in PAH. The proposed research is designed to address these knowledge gaps using a mixed methods approach combining quantitative and qualitative research techniques. The quantitative component will build upon an existing prospective cohort study of patients treated for PAH. The qualitative component will consist of focus group sessions conducted among a subset of patients drawn from the larger cohort. The specific aims are: Aim 1: To determine how quality-of-life relates to clinical measures of disease severity in PAH overtime;Aim 2: To determine if quality-of-life predicts health care utilization, lung transplant, and death in PAH;and Aim 3: To describe the impact of psychosocial factors on quality-of- life in patients with severe PAH. To insure the success of this multi-faceted study, an interdisciplinary team of researchers with expertise in pulmonary vascular disease, survey methods, psychometric analysis, health services research, and qualitative inquiry has been assembled. The proposed research is significant in that it utilizes a novel approach that will quantifiably establish quality-of-life as an important predictor and outcome in PAH, while also qualitatively informing a theoretical model that will assist in the development of future health status instruments. Such research is directly relevant to public health in that it will improve our ability to assess quality-of-life in PAH, thereby enabling us to identify those medical interventions that have the greatest impact on quality-of-life in this understudied population. (End of Abstract)